单轴拉力刺激对人股薄肌腱干细胞炎性因子表达的影响

目的 观察单轴拉力刺激对肌腱干细胞（TDSCs）炎性因子表达的影响.方法 通过胶原酶法和低密度接种法,从人的股薄肌腱中分离TDSCs;流式细胞术检测分离出的TDSCs的表面标记因子;体外诱导检测其多向分化能力.将细胞接种在体外细胞力学加载仪上,分别施加4％、8％和10％的单轴拉力.显微镜观察拉力刺激后的排列情况.荧光定量PCR和Western blot 观察拉力后TDSCs环氧合酶-2（COX-2）和基质金属蛋白酶-1（MMP-1）的基因和蛋白表达情况.结果 从人股薄肌腱中分离出TDSCs,表达CD29、CD44和CD105阳性,CD45和CD14阴性.拉力刺激4h,TDSCs未发生重新排列.4％拉力强度下MMP-1基因表达为0.090±0.007,与0％的0.247±0.032比较显著降低（P ＜0.05）;COX-2基因表达为0.005±0.001,与0％的0.005±0.001比较差异无统计学意义（P＞0.05）.与0％拉力强度比较,8％拉力强度下MMP-1和COX-2基因表达差异均无统计学意义（8％分别为0.168±0.040和0.007±0.001,而0％分别为0.134±0.075和0.006±0.003）（P＞0.05）.10％拉力强度下MMP-1和COX-2基因表达较0％拉力强度比较差异均显著升高（10％分别为0.047±0.003和0.496±0.036,而0％分别为0.011±0.003和0.005±0.003）（P＜0.05）.蛋白表达与基因表达相一致,与0％拉力强度比较,4％拉力强度下COX-2和MMP-1蛋白表达均降低,8％拉力强度下COX-2和MMP-1蛋白表达均无明显变化,10％拉力强度下COX-2蛋白表达升高,MMP-1有微弱升高.结论 不同强度单轴拉力引起炎性因子的表达不同,低强度拉力降低炎性因子表达,高强度拉力升高炎性因子表达.

Statistical damage model for quasi-brittle materials under uniaxial tension

Based on the parallel bar system, combining with the synergetic method, the catastrophe theory and the acoustic emission test, a new motivated statistical damage model for quasi-brittle solid was developed. Taking concrete for instances, the rationality and the flexibility of this model and its parameters-determining method were identified by the comparative analyses between theoretical and experimental curves. The results show that the model can simulate the whole damage and fracture process in the fracture process zone of material when the materials arc exposed to quasi-static uniaxial tensile traction. The influence of the mesoscopic damage mechanism on the macroscopic mechanical properties of quasi-brittle materials is summarized into two aspects, rupture damage and yield damage. The whole damage course is divided into the statistical even damage phase and the local breach phase, corresponding to the two stages described by the catastrophe theory. The two characteristic states, the peak nominal stress state and the critical state are distinguished, and the critical state plays a key role during the whole damage evolution course.

Experimental study on complete stress-deformation curves of larger-size concrete specimens subjected to uniaxial tension

In order to provide parameters for numerical analyses of the huge Three-Gorge concrete dam (2309 m long by 175 m height), complete tensile stress-deformation curves for large-size plain concrete specimens were measured and studied by per-forming uniaxial tensile tests on large-size unnotched specimens (250 mm×250 mm×1400 mm). The specimens were prepared with the three-graded-aggregate materials provided by the client of the Three-Gorge project. To prevent a failure occurring near the ends of the unnotched specimens, both the ends of each specimen (450 mm in length) were cast using a higher-strength concrete than the middle part (i.e., active part). Tensile tests were completed on a specially-designed tensile testing machine, which can be easily re-assembled to accommodate different-size specimens. To make the specimens fail stably, a cyclic loading scheme was adopted after the peak strength was reached. Four of five tests in this study were successful, and four complete tensile stress-deformation curves were obtained. It was found that the post-peak curve of the large-size specimens used in this study is more gradual than those for the small-size specimens reported in the literature.

Unified analytical stressstrain curve for quasibrittle geomaterial in uniaxial tension, direct shear and uniaxial compression

Considering strain localization in the form of a narrow band initiated just at peak stress, three analytical expressions for stressstrain curves of quasibrittle geomaterial (such as rock and concrete) in uniaxial tension, direct shear and uniaxial compression were presented, respectively. The three derived stressstrain curves were generalized as a unified formula. Beyond the onset of strain localization, a linear strain-softening constitutive relation for localized band was assigned. The size of the band was controlled by internal or characteristic length according to gradient-dependent plasticity. Elastic strain within the entire specimen was assumed to be uniform and decreased with the increase of plastic strain in localized band. Total strain of the specimen was decomposed into elastic and plastic parts. Plastic strain of the specimen was the average value of plastic strains in localized band over the entire specimen. For different heights, the predicted softening branches of the relative stressstrain curves in uniaxial compression are consistent with the previously experimental results for normal concrete specimens. The present expressions for the post-peak stressdeformation curves in uniaxial tension and direct shear agree with the previously numerical results based on gradient-dependent plasticity.

单轴、双轴循环拉力对小鼠肌腱源性干细胞肌腱样分化的影响

目的探讨单轴、双轴循环拉力对小鼠肌腱源性干细胞(TDSCs)分化的影响,为临床肌腱损伤后的康复治疗提供理论基础。方法取6~8周龄C57BL/6小鼠10只,无菌条件下暴露双侧后腿至脚掌,显微镜下解剖收集小鼠髌腱和跟腱组织块,体外分离培养细胞,观察第3代细胞的形态特点。(1)取传代至第3代的细胞,采用流式细胞术检测间充质干细胞标志物(CD44、CD90、Sca-1)、内皮细胞标志物(CD34、Flk-1)、造血细胞标志物(CD45),鉴定细胞是否符合TDSCs特点。(2)取传代至第3代的TDSCs进行成骨细胞、软骨细胞和脂肪细胞分化培养,分别采用茜素红、油红和阿尔新蓝染料对培养的三系细胞进行染色,鉴定细胞是否具有多向分化潜能。(3)取传代至第3代的TDSCs接种到硅胶底培养皿上,分为双轴循环拉力组、单轴循环拉力组、对照组3组。双轴循环拉力组细胞使用Flexcell? FX-4000TM柔性基底拉伸加载系统,单轴循环拉力组细胞使用自制拉伸力生物反应器,对照组细胞无拉力。双轴循环拉力组、单轴循环拉力组施加机械负荷组的参数均设置为0.25 Hz、6%的循环拉力,在培养期间进行机械负荷加载,每天加载8 h,共加载6 d。第6天机械负荷刺激结束后,收集3组细胞进行实时荧光定量PCR (qPCR),检测肌腱、成骨、脂肪和软骨相关转录因子的表达。结果显微镜下观察第3代TDSCs形态一致,呈梭形纤维状。(1)流式细胞技术检测结果显示,间充质干细胞标志物CD44、CD90和Sca-1表达阳性、内皮细胞标志物CD34和Flk-1表达阴性、造血细胞标志物CD45表达阴性,符合TDSCs标记鉴定特点。(2)三系分化细胞检测结果显示,提取的细胞成功分化为成骨细胞、脂肪细胞和软骨细胞,验证了提取的细胞具有向成骨细胞、软骨细胞和脂肪细胞分化的潜能。(3)对照组、单轴循环拉力组、双轴循环拉力组3组间比较,肌腱、成骨、软骨、脂肪相关转录因子的相对表达量差异均有统计学意义(P值均<0.05)。组间两两比较:单轴循环拉力组与对照组比较,肌腱、成骨相关转录因子以及脂肪相关转录因子PPARγ的相对表达均增高,软骨相关转录因子的相对表达均降低,差异均有统计学意义(P值均<0.05),而脂肪相关转录因子CEB/P的相对表达差异无统计学意义(P>0.05);双轴循环拉力组与对照组比较,肌腱相关转录因子Scx、Mohawk的相对表达降低,成骨相关转录因子Runx2的相对表达增高、碱性磷酸酶(ALP)的相对表达降低,软骨相关转录因子Sox9相对表达增高、Col2a1的相对表达降低,脂肪相关转录因子的相对表达均增高,差异均有统计学意义(P值均<0.05);单轴循环拉力组与双轴循环拉力组比较,双轴循环拉力组肌腱相关转录因子Scx、Mohawk、Col1a1的相对表达均降低,成骨相关转录因子ALP的相对表达降低,软骨、脂肪相关转录因子的相对表达均增高,差异均有统计学意义(P值均<0.05)。结论单轴循环拉力诱导TDSCs向肌腱细胞、成骨细胞分化,而双轴循环拉力诱导TDSCs向成骨细胞、脂肪细胞、软骨细胞分化。单轴循环拉力的作用下可以促进体外TDSCs向肌腱细胞分化,有利于肌腱组织的再生和损伤后的修复,为临床肌腱损伤后的康复治疗提供了理论依据。

Warm hydroforming of magnesium alloy tube with large expansion ratio

Process of warm tube hydroforming was experimentally investigated for forming an AZ31B magnesium alloy tubular part with a large expansion ratio. Effects of temperature on the mechanical properties and formability were studied by uniaxial tensile test and hydraulic bulge test. Total elongation increases with temperature up to 250℃, but uniform elongation and maximum expansion ratio get the highest value at 175℃. Different axial feeding amounts were applied in experiments to determine the reasonable loading path. A preform with useful wrinkles was then realized and the tubular part with an expansion ratio of 50% was formed. Finally, mechanical condition to produce useful wrinkles is deduced and the result illustrates that useful wrinkles are easier to be obtained for tube with higher strain hardening coefficient value and tubular part with smaller expansion ratio.

MD simulations of loading rate dependence of detwinning deformation in nanocrystalline Ni

Molecular dynamics simulations are performed to investigate the deformation behavior of nanocrystalline Ni with pre-twin atom structure.The simulation sample is composed of four grains with average size 12 nm.The simulation technique of isobaric-isothermal ensemble(NPT) with high pressure is applied to obtain a sample with two circle twins.Under uniaxial tensile and shear loading,as well as different detwinning deformation behaviors are observed.Under uniaxial tension the detwinning deformation is induced by the event of grain growth,and it is supported by local energy analysis.Under the shear loading the detwinning deformation is related to the loading rate.The results show that there may be a critical shear rate.As the shear rate is sufficiently high the circle twin is found to be failed;as the shear rate is less than that rate,the size of circle twin become smaller and gradually approach a constant value.Our simulation results are in good agreement with experiment observation.

Rate-dependent constitutive model of poly(ethylene terephthalate) for dynamic analysis

Uniaxial tensile testing at strain rates ranging from 10-3 to 10-1 s-1 was carried out to study the rate-dependent me-chanical behavior for poly(ethylene terephthalate) (PET) used in the packaging industry. The experimental results show that a rate-dependent plastic behavior exists for PET material. The value of the yield strength was found to increase with the increasing strain rate. A new constitutive model based on the improved Cowper-Symonds rate-dependent constitutive model is proposed to describe the mechanical behavior of PET material in the strain rate ranging from 10-3 to 10-1 s-1, providing more accurate material data for the subsequent simulation analysis of drop test and dynamic buckling. The predictions obtained using the proposed model are compared with experimental results of the improved Cowper-Symonds model. The simulating results of the proposed model agree well with the experimental data. For a low strain rate, the predictions of this model are more precise than those obtained using the improved Cowper-Symonds model. This confirms that the new constitutive model is suitable for describing the me-chanical behavior of PET material at a low strain rate and modeling impact problem.